1. Field of the Invention
The present invention relates to a damper disc assembly that employs both elastic members and friction members for dampening vibration. In particular the invention relates to an improved friction member and improved spring seats used with the elastic members.
2. Description of the Related Art
A clutch disc assembly for use in, for example, an automotive vehicle is typically provided with a disc-like power input plate, an power output hub formed with a radially extending flange, and coil springs disposed between the power input plate and the power output hub so as to limit the relative displacement between them. Alternatively, a separate hub/intermediate plate type damper disc assembly may also be provided. In this type of damper disc assembly, the conventional flange portion is separated from the hub portion and coil springs of low rigidity couple the separated flange and the hub portion.
In the separate hub/intermediate plate type damper disc assembly, the coil springs for coupling the separated flange and the hub portion are disposed within a receptacle formed in the flange portion of the hub side and a receptacle formed in the separated flange. Spring seats are provided on opposite sides of the coil spring. The end surface on the outer circumferential side in the circumferential direction of the spring seat is in contact with the receptacle portion of the flange portion of the hub side and the receptacle portion of the separated flange, respectively.
In the conventional spring seat used in the clutch disc assembly described above, the portion which the receptacles of the separated flange and the flange portion of the hub contact is made a slanting surface with V-shaped cross section. This slanting surface gradually lowers from the radially opposite sides to the inner circumferential side of the spring seat. In other words, the bottom of two of the slanting surfaces extends in the axial direction of the spring seat. The receptacle portion of the flange portion of the hub side and the receptacle portion of the separated flange extend towards the circumferential inner side and are in contact with each of two slanting surfaces, respectively.
When assembling a damper disc, the spring seat is typically already attached to opposite ends of the coil spring. The operators in the assembling line position the spring seats and coil spring within the space defined by the receptacle of the flange portion of the hub and the receptacle of the separated flange. At this time, the spring seat must be properly oriented for installation so that the slanting surface with V-shaped cross section corresponds to each slanting portion of receptacles of the flange portions of the hub side and the separated flange. In other words, the orientation of the spring seats is critical during installation. For example, if the spring seat turned by 90 degrees with respect to the correct orientation, it can not be installed. For this reason, the operators need to be careful about the orientation of the spring seats during installation. The necessity of proper orientation is an opportunity for error and may contribute to operational inefficiencies during assembly.
In other clutch disc assemblies a disc-like power input plate is provided along with a power output hub having a flange integral with its outer circumferential portion, and coil springs disposed between the power input plate and the flange so as to limit the relative displacement therebetween. The flange is provided with window holes formed by, for instance, die-cutting for receiving coil springs. The circumferentially opposite ends of the coil springs are in contact with the respective edge of the window hole. Support portions for supporting the circumferencially opposite ends of the coil spring is formed on the power input plate. With this configuration, when the power input plate are rotated, the torque is transmitted to the hub through the coil springs.
Alternatively, a separate hub/intermediate plate type clutch disc assembly have also been provided. In this type of clutch disc assembly, the conventional flange portion is separated from the hub portion and is couple to it by mean of the coil springs. In this type of clutch disc assembly, a larger twist angular displacement can be produced, and further, two levels of the characteristics of torsion can be obtained. A pair of the spring seats is disposed on the opposite ends of the small coil spring. The flange portion and the hub portion are provided with gear teeth which are circumferentially spaced apart from each other and the gear teeth of the flange portion and the gear teeth of the hub engage together with each other.
In the above described clutch disc assembly described above, the gear teeth of the hub portion are offset toward on the negative side (in the direction opposite to the rotational direction) by positioning off center between each of the gear teeth of the flange portion in a torsion free state. In other words, the amount of twist angular displacement of the hub portion with respect to the flange portion is larger on the positive side (in the rotational direction) and smaller on the negative side.
Such a configuration, under certain conditions, causes unpleasant sounds. It is possible to reduce these sounds by altering the characteristics of twist angular displacement depending on the type/model of the automotive vehicles. Altering the characteristics of twist angular displacement can be carried out by modifying the configurations of the flange portion and the hub portion, however, the production costs associated with manufacturing modified parts is prohibitive.
The above described clutch disc assembly also includes a hysteresis torque generating mechanism which includes friction elements which can be is pressing contact with the flange of hub and conical springs for pressing the friction elements against the flange.
It is desirable that the friction elements of the hysteresis torque generating mechanism are not rotatable relative to either one of the power input plate or the flange for stabilizing the hysteresis torque. Further, in view of operation efficiency, it is desirable that the hysteresis torque generating mechanism is integrally attached to either one of the power input plate or the power output hub.
The friction element with engaging portion engagable with the power input plate and prohibiting the relative rotation with respect to it has been provided. In this device, the friction element and conical spring are integrally mounted to the power input plate by means of the engaging portion.
With this arrangement, the friction element always rotates relative to the power output hub during operation, so that the hysteresis torque generated is stabilized. Further, since the friction element and conical spring are integrally mounted to the power input plate, the devices are portable as one unit, thereby enhancing operation efficiency.
The engaging portion of the friction element described above is elastic and its inter-fitting portion which axially extends is configured to be inter-fitted into the aperture formed on the power input plate. For this reason, the friction element of this type is normally formed by resin molding.
However, since the friction element of resin generally has a low friction coefficient, the sufficient amount of the friction force can not be obtained and, especially, the shock upon speedup/slowdown can not be efficiently absorbed. Also, in the initial condition, since the friction elements do not uniformly contact the power input plate, the friction coefficient becomes unstable. As a result, the desirable amount of the hysteresis torque can not be obtained.